I'm using Catalyst 12.2 on XP with a RadeonHD 5770.
As I said before, Thief Gold is playable although it has some quirks. In my experience it plays better without the HDRadeon fix (included as an extra in Voodoo's tgfix download).
Crashing seems to be centered around saving and reloading and specific objects or effects in the game. As an example, I played the last three-quarters of the third mission (Bonehoard) with absolutely no problems whatsoever. In the fourth mission I was in a library with a desk. Every time I looked at the desk, I got a crash. If I started a new game then reloaded to the library from the front gate of Bafford's mansion in mission 1, I could look at the desk, but if I tried to look at or use any objects on the desk, or even save the game while looking at the desk, I got a crash.
To get around the problem (and I've done this several times in different places) I reloaded, then moved away from the desk to a different area. Not far, but far enough to get some different ambient music, or something -- say, one room away. When I returned, the desk worked normally and no longer caused a crash.
Odd, am I right? But it works. Just go do something else for a couple minutes, them come back.
I'm now at the start of the fifth mission, and while it's been a bit frustrating at times, I've figured out how to avoid the crashing, or at least get around it, so everything's moving along nicely. Killer, killer game BTW.